1. Field of the Invention
The process of drilling wells is both time consuming and exceedingly expensive. In most cases, there is no warranty that the driller will be rewarded at the bottom of the hole. One aspect of the process which adds considerably to the expense is that the entire drill string has to be pulled, from time to time, to change tools, whether to replace a dull tool, or to change tools to change functions, such as, for example, underream a production area. In shallow wells, this task is, of course, less onerous, but with each section of the drill pipe added to the string, the task requires that much more time.
While combining a drill bit and underreamer in a single tool has been attempted, such a tool, by its very nature, has posed problems in the industry in that drilling fluid, commonly referred to as "mud", is pumped down the drill string to lubricate the tool, as well as clean away debris. When tools capable of multiple function, such as the present invention, are introduced, means must be devised for the controlled distribution of drilling mud for lubrication of all of the cutters, as well as actuation and deactuation of the underreamer cutters.
2. Description of Related Art
As mentioned, drill bits and underreamer tools are generally well known in the drilling art. One example of a patented underreamer is found in Thometz et al. U.S. Pat. No. 3,712,854, which is a two-stage underreamer in which the cutter arms are fluid actuated. Thometz suggests, but does not elaborate on, the prospect of combining a drill bit with the underreamer function, and there is certainly no disclosure of an adequate drilling mud distribution system.
Boe U.S. Pat. No. 4,889,197 is illustrative of another type of underreamer employing a different cutter arrangement, and, while being hydraulically actuated, performs that function in a somewhat different manner than Thometz.
Yet another expandable tool is found in Kammerer, Jr. U.S. Pat. No. 3,050,142, and while the intent and purpose of the Kammerer tool is to combine the cylindrical body member and drill string to minimize the number of trips required up and down the hole, it nonetheless illustrates a type of tool which has gained acceptance in the art.
Finally, Furst et al. U.S. Pat. No. 4,660,657, which discusses a combination tool comprising an underreamer and a drill bit, although the objective of the patent is not the provision of such a combination tool.